P. carinii produces an opportunistic infection common in immunocompromised patients. Only two pharmacological agents, trimethoprim sulfamethoxazole and pentamidine are currently used to treat P. carinii; AIDS patients have been observed to suffer adverse reactions to these drugs. New pharmacological agents for treatment of P. carinii could substantially improve the quality of life for AIDS patients. Previous reports in the literature indicate that P. carinii may contain chitin; preliminary findings in our laboratory indicate that chitin is indeed found in the wall of P. carinii. Since chitin is a unique polysaccharide not found in the vertebrate host, it would appear to be an ideal target for pharmacologic therapy. The present study will utilize dexamethasone treated rats which spontaneously develop P. carinii infections. The organism will be cultured in CEL cells as well. Two approaches will be investigated; first, chitin synthesis inhibitors will be tested for their ability to block the proliferation of P. carinii in CEL cells. Second, chitinase conjugates will be investigated as a means of attachment to and killing P. carinii; a variety of delivery modes will be investigated. From a diagnostic point of view, there are no definitive histochemical or immunostaining tests for chitin. Thus, a fast, sensitive method for detection of P. carinii infections may prove useful in the diagnosis of the disease.